3T Pixel Reset Noise Suppression via In-Pixel Feedback Amplifier
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Solution Overview
Problem
Three-transistor (3T) pixels in optoelectronic image sensors suffer from high reset noise, limiting signal-to-noise ratio (SNR) and dynamic range due to kTC noise, and existing active pixel reset methods consume significant power and chip area, with slow reset speeds and limited simultaneous row reset capability.
Innovation Solution
The implementation of an in-pixel reset amplifier that can be dynamically configured as a source follower during signal readout and as a single-stage feedback amplifier during reset, using a pMOS transistor and a bypass switch to bypass the current source load, allowing for simultaneous reset of multiple rows and reducing external loop capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dedicated operational amplifier is coupled to each column for active pixel reset, then kTC noise is suppressed, but power consumption and chip area increase significantly
Solution Approach 1:
The patent combines the reset amplifier function with the pixel circuit itself, integrating the feedback mechanism directly in the pixel rather than using separate column-level amplifiers. This merging eliminates the need for dedicated external amplifiers, thereby reducing power consumption and chip area while maintaining noise suppression capability
Solution Approach 2:
The in-pixel feedback circuit serves multiple functions: it acts as both the reset amplifier for noise suppression and as part of the readout circuitry. This multi-functionality eliminates the need for separate dedicated amplifiers, reducing overall power consumption and chip area requirements
2Object-affected harmful factors
If a dedicated operational amplifier is coupled to each column for active pixel reset, then kTC noise is suppressed, but chip area increases significantly
Solution Approach 1:
The patent merges the reset amplifier functionality into the pixel circuit structure itself, eliminating the need for separate column-level operational amplifiers. This integration dramatically reduces the chip area required while maintaining effective noise suppression
Solution Approach 2:
The patent extracts the feedback mechanism from the external column readout circuitry and places it directly within the pixel circuit. This extraction eliminates the need for large external amplifiers, thereby reducing chip area while preserving noise cancellation capability
3Object-affected harmful factors
If conventional active pixel reset is used, then kTC noise is suppressed, but reset speed is slow
Solution Approach 1:
The in-pixel feedback circuit is prepared and activated simultaneously with the reset operation, allowing the feedback mechanism to immediately counteract kTC noise as it occurs during reset. This preliminary positioning of the feedback mechanism enables faster noise suppression compared to external amplifiers that must be activated sequentially
4Object-affected harmful factors
If conventional active pixel reset is used, then kTC noise is suppressed, but simultaneous row reset capability is limited
Solution Approach 1:
The patent implements independent feedback circuits in each pixel, allowing each pixel to perform reset operations independently and simultaneously. This segmentation of the feedback function into individual pixel-level circuits enables multiple rows to be reset at the same time, dramatically improving productivity compared to column-level feedback approaches
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces reset noise and enhances reset speed, achieving faster and more efficient noise suppression with reduced power consumption and chip area usage, while allowing for simultaneous reset of multiple rows.
Implementation Method 1
a photosensitive medium configured to convert incident photons into charge carriers
Data Source
AI summary
Imaging apparatus includes a photosensitive medium, which is configured to convert incident photons into charge carriers. An array of three-transistor (3T) pixel circuits, coupled to the photosensitive medium, is arranged in rows and columns on a semiconductor substrate and collects the charge carriers from the photosensitive medium. A readout circuitry includes a plurality of column readout lines; each column readout line is coupled to respective outputs of the pixel circuits in a corresponding column of the array and includes a current source load coupled between a constant-voltage supply and the outputs of the pixel circuits, and a bypass switch in parallel with the current source load. Control circuitry alternately opens the bypass switch on each column readout line during a signal readout phase and closes the bypass switch during a pixel reset phase.